From f78ee1aff1184c08b8d82f96fb9077586d1a4ed0 Mon Sep 17 00:00:00 2001
From: Steve Klabnik <steve@steveklabnik.com>
Date: Tue, 21 Apr 2015 11:18:33 -0400
Subject: [PATCH] Document functional update syntax
Fixes #24639
---
src/doc/trpl/structs.md | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/src/doc/trpl/structs.md b/src/doc/trpl/structs.md
index ff249d6043c..fcf928e427c 100644
--- a/src/doc/trpl/structs.md
+++ b/src/doc/trpl/structs.md
@@ -87,3 +87,33 @@ fn main() {
point.y = 6; // this causes an error
}
```
+
+# Update syntax
+
+A `struct` can include `..` to indicate that you want to use a copy of some
+other struct for some of the values. For example:
+
+```rust
+struct Point3d {
+ x: i32,
+ y: i32,
+ z: i32,
+}
+
+let mut point = Point3d { x: 0, y: 0, z: 0 };
+point = Point3d { y: 1, .. point };
+```
+
+This gives `point` a new `y`, but keeps the old `x` and `z` values. It doesn’t
+have to be the same `struct` either, you can use this syntax when making new
+ones, and it will copy the values you don’t specify:
+
+```rust
+# struct Point3d {
+# x: i32,
+# y: i32,
+# z: i32,
+# }
+let origin = Point3d { x: 0, y: 0, z: 0 };
+let point = Point3d { z: 1, x: 2, .. origin };
+```